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Structural changes in poly(lactic acid) caused by γ-radiation

Poly(lactic acid) (PLA) intrigues many scientists, since it is known as a biodegradable polymer with one of the highest consumption volumes of the world. Due to its specific properties, especially those that make it ecologically acceptable, it has a wide application, from food packaging to medical implants. In this study, we used commercially available 3D printing filaments of PLA. The objective of this study was to investigate what type of structural changes are occurring by exposure of PLA to γ-radiation. The main point of our interest was the observation of radical formation and their stability as a function of time. Various total radiation doses were applied: starting from 25 kGy to 300 kGy. Electron spin resonance (ESR), a powerful tool in monitoring radicals, was used as the principal technique. FTIR spectroscopy was applied to check expected changes in vibrational spectra of the treated samples. ESR spectra measured immediately after the irradiation of PLA samples show a relatively strong signal. The radical concentration depends on the applied irradiation dose, while the spectral lineshape appears to be dose independent. Spectra of irradiated samples were compared to those of unirradiated PLA filaments. The loss of the ESR signal, directly related to the decrease of radical concentration, was monitored as a function of time for all applied radiation doses.. Differences in FTIR spectra of irradiated and unirradiated samples are reported and discussed. Results of spectroscopic measurements were supported by those obtained by other techniques.

Poly(lactic acid), PLA, γ-radiation, structure

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